I configured search on a separate app server. Everything went well but the app pool wouldn't stay running. I got the following error in the event viewer:
Application pool decef64cb5444595a2545b4739a42fbe has been disabled. Windows Process Activation Service (WAS) encountered a failure when it started a worker process to serve the application pool.
When I tried to access the search admin page, it displays the following at the top of the page:
Administrative status The remote server returned an error: (503) Server Unavailable.
I am using a domain account to run the service: sp_search
I finally added the sp_search account to the local computer admin group and it worked. I didn't think an application pool service account needed to be in the local admin group.
Edit: it appears my service app pool account has the same issue. It works only when it is a local admin on the server.
I also tried adding the accounts to the GP "log on as service" and "log on as batch job" settings, but it still didn't work.